This invention relates to a biodegradable, lubricative resin composition, and slide bearings and gears molded of such resin composition.
Today, increasingly greater numbers of slide members such as slide bearings and gears are made of plastics rather than metals because they are required to be as lightweight as possible while maintaining sufficient sliding properties.
Preferable plastics materials for molding such slide members include those having some degree of sliding properties (such as low friction and high wear resistance), such as polyamides and polyacetals.
But such plastic products have a problem in that they do much harm to the environment when buried in the ground or dumped in the sea, because most such plastic wastes do not degrade in the ground or water and thus retain their original shapes practically permanently.
Biodegradable polymers are free of this problem. Known biodegradable polymers include poly(.alpha.-hydroxy acids), which turn to oligomers or monomers by being gradually hydrolyzed in the environment, and poly(.beta.-hydroxy alkanoate), poly(.omega.-hydroxy alkanoate) and polyalkylene alkanoate, which are degraded by enzymatic action in vivo or in vitro. Poly(.alpha.-hydroxy acids) include polylactic acid and polyglycol acid. Poly(.beta.-hydroxy alkanoate) includes a copolymer of hydroxyvaleric acid and hydroxybutyric acid. Polyalkylene alkanoate includes a dehydrated condensate of 1,4-butanediole and succinic acid (i.e. polybutylene succinate). Among these polymers, polylactic acid is biodegraded 100% in vivo in several months to one year, and degrades and disappears in a wet environment such as in the ground or seawater in one to several years' time. It is broken down into lactic acids that are harmless to humans and eventually into carbon dioxide and water.
However, not all of these biodegradable polymers can replace conventional plastics materials. In fact, there is not yet known a biodegradable plastic which does not impair any properties required for conventional engineering plastics used for sliding members.
But to protect the environment, it is required to form as many parts of sliding members from biodegradable resins as possible.
An object of the present invention is to provide a lubricative resin composition which is biodegradable, stably low in friction coefficient and high in wear resistance when used as sliding parts, and to provide slide bearings and gears which are biodegradable and have lubricity.